The present invention relates to a wireless radio communications method and, in particular, to a packet data communication method between network nodes.
Broadband wireless networks operating at the multi gigahertz spectrum have the potential of delivering a multitude of services to customers at diverse locations. The high frequency of the spectrum allows the deployment of wireless networks with high capacity using a large amount of bandwidth per network per spatial region. In former times, the radio spectrum was licensed for individual services or uses, such as television bands, amateur radio bands, aviation bands, etc. Within each band, individual users were licensed on a link basis such that all users within a band were licensed. In 1998, the FCC (Federal Communication Commission) departed from this approach and auctioned a large amount of the radio spectrum in the 27 GHz and 31 GHz bands for use in Local Multipoint Distribution Systems (LMDS). Similar spectral bands were opened for use in Canada, Australia, New Zealand and Argentina. In Europe, the radio spectrum between 24.5 and 26.5 GHz was also assigned for multipoint use. Many countries are in the process of opening different bands at the high frequency spectrum between 10 GHz and 40 GHz for use on a territorial basis rather than on a link per link basis. This main difference of approach in licensing the radio spectrum (territorial versus link) enables the network operator to build a network which covers large topographical area and offers connectivity services to those customers in line of sight relation in the region. This is because millimeter wave transmission depends on line of sight between communicating transmitters and receivers.
The new regulatory arrangement after 1988 led to the development of point to multipoint wireless systems. Those systems are based on series of base stations with sectoral transmitters and receivers covering cells split into sectors which include customers whose transceivers are facing towards the base station""s sectoral antenna. Those customers receive the information broadcast downstream from the base station and select the information addressed to them. On the upstream side, in the TDMA (time division multiple access) mode, the base station assigns time slots or, in the FDMA (frequency division multiple access) mode, frequency slots to each one of the remote customers"" transceivers to allow polling information based on the amount of information needed to be transmitted by those customers.
The data protocols for communication are known as xe2x80x9clayersxe2x80x9d because each layer is a level of the communications system, having its own rules and sometimes having people whose only concern is with operation of that level. The concept of xe2x80x9clayersxe2x80x9d is explained in many data communication texts and may be summarized as follows. Starting with hardware, considered as the lowest layer, the equipment for making radio communication possible, is known as the xe2x80x9cphysical layerxe2x80x9d, while the highest level, which is the application run by the consumer, is known as the xe2x80x9capplication layerxe2x80x9d. Immediately above the physical layer is the xe2x80x9clink layerxe2x80x9d which manages the transmission of data without error. Then follows the xe2x80x9cnetwork layerxe2x80x9d which performs a routing function to set up connections across a network. Then follows the xe2x80x9ctransport layerxe2x80x9d which provides addresses to the network layer and determines the size of units in which data are transported. Next follows the xe2x80x9csession layerxe2x80x9d which arranges commands between terminals, such as xe2x80x9cstartxe2x80x9d and xe2x80x9cfinishxe2x80x9d. Just below the application layer and above the session layers is the xe2x80x9cpresentation layerxe2x80x9d which defines the format of the data presented, overcoming differences in the requirements of different terminals. In wireless networks, there is an additional layer, the xe2x80x9cmedium access control layerxe2x80x9d, or MAC layer, which is used within the network topology as a protocol for data communication between transceivers of interconnected nodes on the network. In the hierarchy of layers described above, the MAC layer would be between the physical layer and the link layer, acting as an interface between the two. In the past, the medium access control (MAC) layer for point to multipoint (PMP) cellular systems was relatively simple and has been in use for many wireless systems, both on the ground, in cellular mobile systems and broadband systems, as well as satellite to ground (VSAT) systems.
The advantage of a point to multipoint (PMP) network with a MAC layer is its simplicity. The main disadvantage of PMP system arises because of the broadcast nature of the downstream link and the polling of the upstream link. When the base station transmits in a certain frequency and time slot (TDMA), all the customers in the sector except the one that receives information are blocked from receiving any information. In the upstream direction, only one customer can transmit at a certain time on a certain frequency. Thus, when the number of customers in a sector increases, the average data rate available per customer decreases.
The second deficiency of the PMP system is the need to establish expensive base stations at a high positions with a good line of sight to all customers. This demands up-front investment.
The third disadvantage comes from the cellular nature of the PMP MAC layer. The nodes can only communicate with their base station sectoral transceiver, and thus no repeating or route diversity can take place. If a line of sight does not exist from a base station to subscriber units, a new base station should be constructed so that all customers can be connected.
In U.S. Pat. No. 5,903,566 to G. Flammer, a multi-node mesh topology wireless network is disclosed for transmitting large data files, block by block. The transmission protocol involves checking the validity of requested blocks of code. For invalid blocks, the source node frees its packet transmit buffer and the process ends. For a valid block, the source node send the block to the destination node then frees its packet transmit buffer and the process ends. The communications protocol for transfer of blocks is not specified.
In cable applications, mesh topology networks are avoided because for xe2x80x9cnxe2x80x9d nodes, n(nxe2x88x921)/2 circuits are required to connect all nodes. However, mesh topology networks are ideal for broadband wireless applications especially when packet data are used for data transmissions, such as in IP (Internet protocol) networks. The current invention relates to a new type of space and time switched MAC layer protocol designed to enable efficient data transmission particularly in mesh topology networks, or other type of network topology on a packet basis.
The advantages of a mesh network are as follows: (1) The network allows repeating information between the nodes thus enables reliable connections between customers and a backbone access point (BAP) via other nodes in the area with whom line of site (LOS) communication can be established, thus achieving high coverage of the relevant area. (2) The network is built around the customers. The network bandwidth capacity increases as the number of nodes (customers) joining the network increases, due to the creation of multiple parallel paths for the data flow. (3) Route diversity and load balancing is enabled by the availability of multiple routes from nodes to other nodes.
The difficulty of implementing this system is the need to have an algorithm to control and synchronize the data transmission between the nodes based on their relative location with an available line of sight distance and an available link, as well as possible interference from burst data traffic originating and terminating at other nodes. In the IP type of network, data packets are randomly generated with random origination and destination cells. Thus, optimal traffic coordination should be adjusted on a packet by packet basis. In addition, in contrast to physically connected networks of fiber or copper, a wireless mesh may have a transceiver and directional antenna with multiple beams and the ability to switch between them. Thus, a space and time switched MAC algorithm should take into account the propagation delay between the different nodes, the queuing of data with the different addresses at each node, the synchronization of the time of transmitting from multiple nodes and the time of reception at multiple different nodes at different delays based on the location of the destination nodes.
This invention features an adaptive space and time switched (STS) MAC protocol design to efficiently allow the implementation of mesh networks with IP type of packet data flow between the network nodes in peer-to-peer communication as well as node-to-BAP and BAP-to-node. The network can operate with TDD (time division duplex wireless radios) operating on the same frequency or at multiple frequencies at different links simultaneously. The STS MAC protocol assigns capacity based on traffic load.
The basic principle of the STS MAC protocol of the present invention is the use of synchronous schedule information as a control channel between the nodes to assign asynchronous variable length packet data slots in between the schedule information time slots. The available data slots are adaptively assigned by each recipient node to the data initiator node based on requested time slots by the initiator and the available time slots of the recipient.
The adaptive STS MAC protocol of the present invention is designed to efficiently support high-bandwidth communication in networks with the following structure: (1) nodes with some wireless connectivity forming a partially (or fully) connected mesh. (2) One or more special nodes, known as backbone access points (BAPs), that connect the wireless mesh to the IP backbone. The nodes in the network have the following capabilities: (1) Each node is capable of steering its receiving and transmitting direction beam antenna to none or one or more of a fixed number of sectors. (2) Signals arriving on different sectors do not interfere with each other. (3) Communication is half-duplex, and a node may communicate on only one sector at a time.
The current adaptive STS MAC algorithm invention enables the creation of multiple simultaneous transmission links between subgroups and peers of nodes in the network based upon the momentary burst of packet traffic load initiated in multiple network nodes and having multiple variable destination addresses, thus allowing dramatic increases in the efficient use of the spectrum at a given spatially covered region, route diversity and load balancing for packet carried information.